Early oral language development provides the foundation for later school achievement and literacy. In some children that foundation is weak, placing them at risk. This is particulary the case for bilingual children, who are overrepresented among children whose early oral language skills compromise their opportunties for later academic success. Understanding influences on monolingual and bilingual development is, therefore, a public health concern. The broad aim of the proposed research is to address this concern by increasing scientific understanding of the external causes and internal processes that produce individual differences in the early language development of monolingual and bilingual children. The proposed research will test the hypothesis that language input influences the development of phonological memory, which, in turn, influences language development. Although relations between phonological memory and language development are well established, very little work has investigated influences on the development of phonological memory itself. Furthermore, research on phonological memory is largely confined to monolingual children over the age of 4 years. These gaps may be due, in part, to a lack of assessment instruments. In preliminary work, the Pis have developed a procedure for assessing phonological memory in children younger than 2 years. The specific aims of the proposed research are: (1) to establish the reliability and validity of this assessment procedure, including extending it to Spanish- English bilingual children, and (2) to use this procedure in order to investigate the relations among language input, phonological memory, and early monolingual and bilingual development. One short-term longitudinal study is proposed. For 50 monolingual English-learning children and 50 Spanish- and English-learning bilingual children, language input, phonological memory, and language development will be assessed at 22 months and language development will be assessed again at 25 months of age. Concurrent and predictive relations among these variables will be tested. The outcomes of this project will advance our understanding of the role of language input and phonological working memory in early monolingual and bilingual language development and will provide the first steps toward the development of tools to identify bilingual children at risk for later language disorders.